Method for producing a stator blade and stator blade

ABSTRACT

A method for producing a turbine vane with a vane airfoil and a vane root is provided to achieve a higher efficiency for a turbine. The method includes: a) production of a vane airfoil and a vane root as separate parts; b) introduction of a cooling air opening into the vane airfoil; and c) joining the vane airfoil and vane root together after step b).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2013/064886 filed Jul. 15, 2013, and claims the benefitthereof. The International Application claims the benefit of GermanApplication No. DE 102012213017.9 filed Jul. 25, 2012. All of theapplications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a method for producing a turbine blade having ablade airfoil and a blade root. It also relates to a turbine blade ofthis kind.

BACKGROUND OF INVENTION

A turbine is a turbomachine which converts the internal energy(enthalpy) of a flowing fluid (liquid or gas) into rotational energy andultimately into mechanical drive energy. A part of the internal energyof the fluid flow is extracted therefrom by the laminar flow, which isas swirl-free as possible, around the turbine blades, said part of theinternal energy being transferred to the rotor blades of the turbine.Via the latter, the turbine shaft is then set into rotation, and theuseful power is transmitted to a coupled working machine, for example toa generator. The rotor blades and the shaft are part of the movablerotor of the turbine, said rotor being arranged within a housing.

As a rule, a plurality of blades are mounted on the shaft. Rotor bladesmounted in a plane each form a blade wheel or rotor wheel. The bladesare profiled in a slightly curved manner, similarly to an airplane wing.Upstream of each rotor wheel there is usually a stator wheel. Thesestator blades project from the housing into the flowing medium and causeit to swirl. The swirl (kinetic energy) generated in the stator wheel isused in the subsequent rotor wheel in order to set the shaft, on whichthe rotor wheel blades are mounted, into rotation.

The stator wheel and rotor wheel together are designated a stage. Often,a plurality of such stages are connected in series. Since the statorwheel is stationary, the stator blades thereof can be fastened both tothe inside of the housing and to the outside of the housing and thusprovide a bearing for the shaft of the rotor wheel.

Both stator blades and rotor blades of the turbine usually comprise, inaddition to the aerodynamically active actual blade airfoil, a bladeroot, which is also known as a platform, is widened compared with theblade airfoil and has fastening devices for fixing each particular bladefor example to the rotor or to the housing. The blade root and bladeairfoil are usually cast together in one piece during the productionprocess and subsequently provided with a metal coating.

In order to cool the components, which are subjected to hot gas, of aturbine, in particular of a gas turbine, film cooling, inter alia, isused. This also applies for the turbine blades. In this case, thecoolant—typically air—is guided through cylindrical or diffuser-likecooling-air openings onto the surface to be cooled in order to form aprotective cooling film. The optimal cooling efficiency is obtained inthat the cooling-air openings are inclined with respect to the surface,depending on the local flow conditions, along the flow lines.

During the production process, the cooling-air bores are introducedpredominantly by laser or erosion methods. In the case of turbine statorblades, the accessibility for the laser or erosion tool is severelyrestricted in the region of the transition from the blade airfoil to theplatform on account of the concave edge that occurs there.Three-dimensionally shaped blade airfoils having an angle between thepressure side of the blade airfoil and the platform of less than 90° andflow lines that are influenced by secondary flow effects make theintroduction of optimally oriented cooling-air bores impossible.

Since the introduction of optimally oriented borers having a maximumcooling efficiency was not hitherto possible, the poorer cooling actionhad to be compensated by an increased number of non-optimal borers. As aresult, the consumption of cooling air was increased and the aerodynamicefficiency of the row of blades reduced. Both result in impairment ofthe turbine efficiency.

Furthermore, EP 2 151 544 A2 discloses siting cooling-air openings closeto the platform on the blade airfoil, in order to guide the cooling airflowing out therethrough onto the platform in order to allow filmcooling there.

Moreover, EP 1 176 284 A2 discloses producing the turbine stator-bladesegments in a modular manner in that a plurality of blade profiles areproduced separately and are then welded to an outer ring and an innerring.

SUMMARY OF INVENTION

It is therefore an object of the invention to disclose a method forproducing a turbine blade and a turbine blade with which greaterefficiency of a turbine can be achieved.

With regard to the method, this object is achieved according to theinvention in that the method comprises the following steps of: a)producing a blade airfoil and a blade root as separate components, b)introducing at least one cooling-air opening into the blade airfoiland/or into the blade root, or introducing at least two openings, atleast one of which is arranged in the blade root and in the bladeairfoil in each case, and c) assembling the blade airfoil and blade rootafter step b).

The invention is in this case based on the consideration that improvingthe efficiency of the turbine could be achieved in that the cooling-airbores could be introduced precisely in the region of the transition fromthe blade airfoil to the platform in an optimized manner with regard tothe flow lines of the medium flowing around. However, this is onlypossible if the corresponding tools for introducing the openings havesufficient freedom of movement. This is achievable when the platform orblade root and blade airfoil are produced as separate parts and areassembled only when the openings have been introduced. Thus, theopenings can be introduced through the blade root into the blade airfoilwithout impedance or the openings can be introduced through the bladeairfoil into the blade root without impedance in each case in anydesired flow-line optimized arrangement.

In an advantageous configuration, the production of the blade rootand/or blade airfoil takes place by casting. As a result, production ofthe components in an exact form with little fault tolerance is ensured.

The introduction of the cooling-air openings advantageously takes placeby laser and/or by means of electrical discharge machining. As a result,both the axis of the openings and the shape thereof can be controlled ina particularly easy manner.

In an advantageous configuration, the axis of the cooling-air opening isdirected toward the blade root at the outer side of the blade airfoil orthe axis of the cooling-air opening is directed toward the blade airfoilat the outer side of the blade root. Such openings are necessaryprecisely in the region of the concave edge between the blade airfoiland platform in order to ensure an optimal orientation of thecooling-air flow along the hot-gas flow lines. At the same time, theyare particularly easy to produce with the described method since theblade root no longer impedes the introduction tool and the latter isfreely movable.

In a further advantageous configuration, the method comprises theadditional step of: d) coating a region of the blade root and bladeairfoil with a coating.

As a result, following the assembly of the blade root and blade airfoil,a continuous coating which increases the thermal and/or mechanicalresilience of the component can be applied.

In this case, it can be problematic that, in the described method, thecoating only takes place once the cooling-air openings have beenintroduced. This can result in local clogging of the cooling-airopenings. If the axis of the cooling-air bores is oriented counter tothe coating direction, this risk can be minimized. However,advantageously, the cooling-air opening is configured in a conicalmanner. As a result, the metal layer within the opening does not have aneffect on the flow of cooling air. A conical configuration is possiblewithout great effort in particular in the case of introduction by meansof laser.

In an alternative or additional configuration of the method, itcomprises the additional step of: e) removing the coating over thecooling-air opening by laser and/or by means of electrical dischargemachining.

Since deep boring is no longer carried out here, but merely surfaceremoval, such great movability of the tool is not necessary, and so theremoval is also possible after assembly and coating of the component. Tothis end, all that is necessary is to know the precise position of theopening.

A turbine blade is advantageously produced with the described method.

With regard to the turbine blade, the object is achieved in that theturbine blade has a blade airfoil and a blade root, wherein the bladeairfoil has a cooling-air opening, the axis of which is directed towardthe blade root at the outer side of the blade airfoil.

A turbine advantageously comprises a turbine blade of this kind.

The advantages achieved by the invention arise in particular in thatparticularly high flexibility with regard to the orientation of the axisof the opening is achieved as a result of the introduction of thecooling-air openings in the separate blade airfoil following casting,and so the cooling-air bores can be oriented in an optimized manneralong the flow lines of the hot gas, and the cooling efficiency and thusalso the efficiency of the turbine is increased. Even very complex 3Dgeometries can be cooled effectively by way of the described method.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail with reference to a drawing,in which:

FIG. 1 shows a gas turbine in longitudinal partial section,

FIG. 2 shows a stator blade according to the prior art in top view,

FIG. 3 shows a stator blade according to the prior art in section,

FIG. 4 shows a stator blade with cooling holes introduced beforeassembly of blade airfoil and blade root in top view, and

FIG. 5 shows a stator blade with cooling holes introduced beforeassembly of blade airfoil and blade root in section.

DETAILED DESCRIPTION OF INVENTION

Identical parts are provided with the same reference signs in all thefigures.

FIG. 1 shows a turbine 100, here a gas turbine, in a longitudinalpartial section. The gas turbine 100 has in its interior a rotor 103,also referred to as turbine rotor, that is mounted so as to rotate abouta rotation axis 102 (axial direction). An intake housing 104, acompressor 105, a toroidal combustion chamber 110, advantageously anannular combustion chamber 106, having a plurality of coaxially arrangedburners 107, a turbine 108 and the exhaust housing 109 follow oneanother along the rotor 103.

The annular combustion chamber 106 communicates with an annular hot-gasduct 111. There, for example four turbine stages 112 connected in seriesform the turbine 108. Each turbine stage 112 is formed from two bladerings. As seen in the flow direction of a working medium 113, a row 125formed from rotor blades 120 follows in the hot-gas duct 111 of a row ofstator blades 115.

The stator blades 130 are in this case fastened to the stator 143,whereas the rotor blades 120 of a row 125 are attached to the rotor 103by means of a turbine disk 133. The rotor blades 120 thus formconstituent parts of the rotor 103. Coupled to the rotor 103 is agenerator or working machine (not illustrated).

During operation of the gas turbine 100, the compressor 105 sucks in air135 through the intake housing 104 and compresses it. The compressed airprovided at the turbine-side end of the compressor 105 is passed to theburners 107, where it is mixed with a fuel. The mixture is then burnt inthe combustion chamber 110, forming the working medium 113. From there,the working medium 113 flows along the hot-gas duct 111 past the statorblades 130 and the rotor blades 120. At the rotor blades 120, theworking medium 113 is expanded in a pulse-transmitting manner, such thatthe rotor blades 120 drive the rotor 103 and the latter drives theworking machine coupled to it.

During operation of the gas turbine 100, the components exposed to thehot working medium 113 are subject to thermal stresses. The statorblades 130 and rotor blades 120 of the first turbine stage 112 as seenin the direction of flow of the working medium 113, in addition to theheat shield elements lining the annular combustion chamber 106, aresubject to the greatest thermal stresses. In order to withstand thetemperatures that prevail there, they are cooled by means of a coolant.Similarly, the blades 120, 130 can have coatings protecting againstcorrosion (MCrAlX; M=Fe, Co, Ni, rare earths) and heat (thermalinsulation layer, for example ZrO₂, Y₂O₄—ZrO₂).

A stator blade 130 according to the prior art is illustrated in top viewin FIG. 2 and in partial section in FIG. 3. With regard to FIG. 1, thestator blade 130 has a stator-blade root 145 facing the internal housing138 of the turbine 108, and a stator-blade head 147 opposite thestator-blade root 145.

The stator-blade head faces the rotor 103 and is fastened to a fasteningring 140 of the stator 143. The stator blade 130 is configured in ahollow manner. A cooling medium, typically air, circulates in theinterior space 131.

The stator blade 130 has, in particular at the stator-blade airfoil 149located between the stator-blade root 145 and stator-blade head 147, amultiplicity of cooling-air openings 151. In the prior art, thecooling-air openings 151 are introduced into the stator blade 130, whichis cast in one piece. However, the flexibility of the tool forintroducing the cooling-air openings 151 is in this case restricted, inparticular in the region of the transition between the stator-blade root145 and stator-blade airfoil 149, where a concave edge 153 arises. Thus,it was previously only possible to introduce cooling-air openings 151 ofwhich the axis 155 is not directed toward the stator-blade root 145. InFIGS. 2 and 3, arrows show the direction of flow of cooling air K andhot gas H. As FIG. 3 clearly shows, the directions of flow are partiallyin opposite directions, and so optimum cooling is not ensured and theconsumption of cooling air is increased.

Here, the stator blade 130 shown in FIGS. 4 and 5, which are analogousto FIGS. 2 and 3, respectively, provides a considerable improvement.Here, the axis 155 of the cooling-air opening 151 is directed toward thestator-blade root 145 in the region of the edge 153. As a result, theflow of cooling air K is directed along the flow lines of the hot gas Hand substantially improved efficiency of the gas turbine 100 isachieved.

This arrangement of the cooling-air openings 151 is enabled by theproduction method, which is explained in the following text. First ofall, the stator-blade airfoil 149 and stator-blade root 145 are castseparately. Then, the critical cooling-air openings 151 are introducedin the region of the edge 153 by means of laser or electrical dischargemachining. The tool is in this case freely movable. Subsequently, theblade root 145 and blade airfoil 149 are connected, for example welded,at the seam 157 shown in FIG. 5.

Subsequently, the stator blade 130 is coated, for example with a metallayer. In this case, the cooling-air openings 151 can become cloggedwith the coating material. In order that no impairment of thecooling-air flow arises here, the cooling-air openings 151 areconfigured in a conical manner. Alternatively or in addition, thecoating over the cooling-air openings 151 can subsequently be removedagain by means of laser or electrical discharge machining. At the sametime, further cooling-air openings that are non-critical with regard toaccessibility can be introduced.

A stator blade 130 manufactured in such a way increases the efficiencyof the gas turbine 100 on account of the improved cooling action.

1.-10. (canceled)
 11. A method for producing a turbine blade having ablade airfoil, a blade root and a region with restricted accessibilityfor a tool for introducing cooling-air openings, said region having aconcave edge in the transition between the blade root and blade airfoil,the method comprising: a) producing a blade airfoil and a blade root asseparate components, b) introducing at least one cooling-air openinginto the blade airfoil and/or into the blade root in said region, and c)assembling the blade airfoil and blade root after step b), wherein theaxis of the cooling-air opening is directed toward or away from theblade root at the outer side of the blade airfoil.
 12. The method asclaimed in claim 11, wherein the production of the separate componentsaccording to step a) takes place by casting.
 13. The method as claimedin claim 11, wherein the introduction of the at least one air-coolingopening according to step b) takes place by laser and/or by electricaldischarge machining.
 14. The method as claimed in claim 11, furthercomprising: d) coating a region of the blade root and blade airfoil witha coating.
 15. The method as claimed in claim 14, wherein thecooling-air opening is configured in a conical manner.
 16. The method asclaimed in claim 14, further comprising: e) removing the coating overthe cooling-air opening by laser and/or by electrical dischargemachining.
 17. A turbine blade produced by the method as claimed inclaim
 11. 18. A turbine having a turbine blade as claimed in claim 17.